The present invention relates to a clamping device. More particularly, the present invention relates to a hybrid type clamping device in which a hydraulic drive system used for a large clamping device and an electric drive system used for a small clamping device are combined with each other. Further, the present invention relates to a method of increasing and decreasing hydraulic pressure used in this clamping device. Furthermore, the present invention relates to a method of releasing a mold.
Conventionally, main stream clamping devices used for injection molding machines or die casting machines are hydraulic drive systems such as direct pressure type clamping devices or toggle type clamping devices. Recently, in order to meet the demand of saving energy and making the working environment clean, an electric drive type clamping device, in which a mold can be opened and closed when a rotary motion of a servo motor is converted into a linear motion of the mold by a ball screw nut, has been widely used, especially in the field of small molding machines.
However, although this small clamping device in which the electric drive system is used can meet the demand of saving energy and making the working environment clean, when the size of this small clamping device is proportionally increased so that the electric drive system can be applied to a large clamping device, the size of the clamping device cannot be increased very much because an increase in the size of a servo motor, and of a ball screw, are restricted. In order to solve the above problems, a hybrid type clamping device, in which an electric drive system is used for a mold opening and closing means and a hydraulic system is used for a clamping force generating means, has been devised.
For example, Japanese Unexamined Patent Publication No. 6-246806 discloses an example of the hybrid type clamping device in which a metallic mold is opened and closed when a movable platen is moved by a screwing motion of a male screw conducted by an AC servo motor, and a clamping motion conducted after the mold has been closed is conducted by a hydraulic means. This hydraulic clamping device is composed as follows. At the back of the movable platen, a hydraulic operating board is arranged which includes a closed chamber having a tightly closed bladder into which hydraulic fluid is charged. After the hydraulic operating board has been locked together with a movable platen, the male screw member is further moved by an electric motor. Due to the foregoing, the tightly closed bladder is pressurized, so that a clamping force is given to a metallic mold by a piston and via the movable platen. In the case of opening the metallic mold, the male screw member is reversed so that the movable platen can be drawn in.
In the conventional hybrid type clamping device described above, while the tightly closed bladder is being pressurized by the male screw in the closed chamber, the pressurizing action is maintained when the male screw member is screwed by an AC servo motor by a ball screw mechanism. Further, both the mold releasing and the mold opening are conducted when the male screw member is screwed in the same manner. Therefore, in the working time when the mold is opened and closed and when the clamping force is given to the mold and when the mold is released, a load must be always given to the electric motor which is a drive source. Therefore, it is impossible to sufficiently accomplish energy saving. Further, since both the electric drive system and the hydraulic drive system are jointly used, the structure of the clamping device becomes complicated, and the frequency of mechanical breakdown is increased.
The above conventional hybrid type clamping device is composed in such a manner that the tightly closed bladder is pressurized by the male screw in the closed chamber. Therefore, unless air is completely removed from the tightly closed bladder when the tightly closed bladder is charged with hydraulic fluid, the clamping force cannot be appropriately given to the mold. It is very difficult to form the tightly closed bladder into which hydraulic fluid is charged in accordance with a volume of the stationary closed chamber. Further, as the tightly closed bladder is deformed into a recessed shape, there is a possibility that the bladder is damaged and the hydraulic fluid leaks out from the bladder. Therefore, it is impossible to increase the clamping force.
Further, the clamping device used for a conventional injection molding machine or die casting machine is composed in such a manner that a stationary platen and a movable platen, to which metallic molds are respectively attached, which are connected with each other by tie rods, are fixed to each other at a mold closing position by a platen lock means. Usually, the platen lock means is composed of a pair of split nuts capable of being opened and closed. When the pair of split nuts are engaged with ring grooves or screw grooves, the movable platen can be fixed and held at the mold clamping position.
In this connection, when a metallic mold is changed, the thickness (die-height) of the metallic mold is changed. Therefore, the mold closing position is naturally changed, and the lock position of the movable platen is also changed. When the die-height is changed as described above, the pitch of engagement of a split nut with a tie rod is shifted in some cases. Accordingly, there is usually provided a die-height adjusting mechanism.
As a conventionally well known die-height adjusting mechanism, as disclosed in Japanese Examined Patent Publication No. 44-16008, there is provided a mechanism in which tie rods are arranged so that they can be moved in the axial direction with respect to a stationary platen so that a phase shift caused between a split nut and the tie rod can be adjusted. Further, as disclosed in Japanese Unexamined Patent Publication No. 11-235741, there is provided a mechanism in which a clamping cylinder is fixed onto a mount moving when a mold is opened and closed, and a movable platen capable of moving on this mount is connected to the clamping cylinder, and when a phase shift is caused between a split nut and a tie rod at a mold closing position, a distance between the clamping cylinder and the movable platen is adjusted so that the die-height can be adjusted.
However, the former mechanism is disadvantageous in that the tie rod must be made movable with respect to the stationary platen, so that the size of the device is increased and the clamping accuracy is deteriorated. The latter mechanism is disadvantageous in that a large-scale device is required for adjusting the die-height. Further, it is necessary to compose the device in such a manner that while the clamping cylinder is being moved together with the movable platen, the distance between them must be made variable.
In the case of a booster-ram type clamping device, the mold opening is conducted in a front hydraulic chamber of the clamping cylinder. Therefore, the accuracy of the entire inner face of the clamping cylinder must be high, and further the diameter is extended. Accordingly, it is hard to conduct precision machining, which results in increasing the manufacturing cost. In the case where the clamping cylinder, the diameter of which is large, is used for opening the mold as described above, the total length of a die casting machine or an injection molding machine is extended, and it becomes difficult to install the die casting machine or the injection molding machine in a small space.
In order to solve the above problems, Japanese Unexamined Patent Publication No. 10-94864 discloses the following arrangement. As shown in FIGS. 31 and 32, the metallic mold attaching plate 3 is put and held on the stationary platen 2, at a plurality of corners of which the tie rods 1 are provided, and the cylinder holes 4 open to the metallic mold attaching plate 3 side are formed on the stationary platen 2. Further, there are provided rams 5 which are slidably engaged with the cylinder holes 4. Furthermore, the tightly closed bladder 6 (shown in FIG. 32), to which hydraulic pressure is applied, is provided in each cylinder hole 4. When hydraulic pressure in the tightly closed bladder 6 is increased, a pushing force is given via the ram 5 so that the metallic mold attaching plate 3 can be pushed to the stationary metallic mold 7 side.
However, when the aforementioned tightly closed bladder 6 is used, the following problems may be encountered. In the case where hydraulic oil is supplied into the tightly closed bladder 6 so as to expand the tightly closed bladder 6 and push the ram 5, or in the case where hydraulic oil is discharged from the tightly closed bladder 6 so as to retract the ram 5 and contract the tightly closed bladder 6, when the tightly closed bladder 6 is repeatedly expanded and contracted, as shown in FIGS. 33A and 33B, a portion of the tightly closed bladder 6 is pushed into clearance H1 between the stationary platen 2 and the ram 5. When the device is used in this state over a long period of time, the tightly closed bladder 6 is finally damaged.
In view of the above conventional problems, the present invention has been accomplished. It is an object of the present invention to provide a compact clamping device and a method of releasing a mold characterized in that: while energy saving is sufficiently accomplished, a high clamping force is generated; and while a hydraulic source is used in common between the clamping pressure mechanism and the mold releasing mechanism, a mold releasing motion can be conducted separately from the clamping mechanism.
Further, another object of the present invention is described as follows. A mold releasing force is given by an electrically driven ball screw mechanism for opening and closing a mold and, while the energy consumption of the electrically driven ball screw mechanism is reduced, the electric driving and the hydraulic driving are preferably combined with other so as to save energy in the processes of clamping and releasing the mold. It is another object of the present invention to accomplish saving in the entire energy consumption.
It is still another object of the present invention to provide a pressurizing mechanism in which hydraulic oil is charged and pressure is generated by the expansion and contraction of hydraulic oil, and this pressurizing mechanism has a structure by which air can be completely removed from the mechanism. It is still another object of the present invention to provide a clamping device in which the above pressurizing mechanism is utilized. In addition to that, it is still another object of the present invention to provide a compact clamping device in which the pressurizing mechanism is utilized while energy can be sufficiently saved and a high intensity clamping force can be generated.
It is still another object of the present invention to provide a pressurizing mechanism of a clamping device characterized in that: the total length of a die casting machine or an injection molding machine can be reduced to as small as possible; the installing space is reduced; the clamping motion can be quickly conducted; and the durability of the mechanism is high.
It is still another object of the present invention to provide a clamping device characterized in that: the structure is very simple; and the die-height can be appropriately adjusted.
It is still another object of the present invention to provide a method of increasing and decreasing hydraulic pressure for clamping capable of realizing energy saving and generating a high intensity clamping force. It is still another object of the present invention to realize saving energy in the clamping process by reducing energy consumption of a drive source after hydraulic pressure has been increased to a value necessary for a clamping force and also by maintaining a pump motor in a state of no load so that energy saving can be accomplished in entire energy consumption. It is still another object of the present invention to prevent the occurrence of vibration and abnormal sound caused when pressure is suddenly reduced in the case of decreasing a clamping force.
It is still another object of the present invention to provide a clamping device characterized in that: hydraulic energy can be transmitted to the clamping device from a hydraulic pressure generating mechanism arranged outside via a hydraulic circuit while hydraulic pressure generating mechanism is not being incorporated into the clamping device; the structure is simple; and the property of saving energy is high and the accuracy of control is excellent.
In order to accomplish the above objects, in an embodiment of a clamping device of the present invention, a pressurizing mechanism comprises: a movable platen having a movable metallic mold, arranged to be capable of going forward and back; a stationary platen having a stationary metallic mold, arranged opposite to the movable platen; a pressure plate arranged between the stationary platen and the stationary metallic mold, the stationary metallic mold being attached to the pressure plate; a piston slidably engaged in a cylinder arranged in the stationary platen, the piston being capable of protruding toward the pressure plate; a bladder arranged between the piston and the cylinder of the stationary platen, the bladder being expanded and contracted when pressure is supplied and discharged, so that clamping can be conducted between the movable and the stationary metallic die via the piston; and a soft protective member interposed between the piston and the bladder, capable of filling a gap formed between them when the bladder is expanded. When the piston is protruded by the expansion of the bladder, a pressure force for clamping is given between the movable metallic mold and the stationary metallic mold via the pressure plate. Further, intrusion of the bladder into the gap is prevented by the sealing action of the soft protective member so that the bladder can be prevented from being damaged.
Another embodiment of a clamping device of the present invention is composed as follows. A stationary platen and movable platen, which are connected to each other by tie rods, to which metallic molds are attached, can be opened and closed by an electrically driven ball screw mechanism. One of the above platens is composed of a platen body and a pressure plate attached to the platen body, the pressure plate being capable of coming into contact with and separating from the platen body, at least in a range of a clamping stroke. The clamping device includes a pressurizing mechanism for clamping between the platen body and the pressure plate. The pressurizing mechanism is composed in such a manner that when a bladder, into which hydraulic oil can be introduced, and arranged in a cylinder, is expanded and contracted, a piston can be pushed out. An insert die, the shape of which is identical with that of the internal shape of the bladder, is housed in the bladder. A hydraulic path is formed in the insert die. A ball screw member of the electrically driven ball screw mechanism is supported while being capable of moving in the axial direction. A brake means for braking rotation is provided in the ball screw member. A mold releasing cylinder mechanism for generating a mold releasing force in the axial direction is connected to it. A hydraulic pressure supply source is commonly used between this mold releasing cylinder mechanism and the aforementioned bladder. When a hydraulic oil path is changed over, the mold releasing cylinder mechanism can be operated.
In this structure, the mold releasing cylinder mechanism is composed in such a manner that hydraulic oil in the clamping hydraulic circuit can be supplied to the mold releasing cylinder mechanism. It is preferable to adopt the following structure. In the hydraulic path to the mold releasing cylinder mechanism, there is provided a hydraulic pressure containing means for containing hydraulic pressure at a position of the origin of the ball screw member so that a movement in the axial direction can be restricted.
In the above structure, the pressurizing means includes a cylinder section and a piston which is housed in the cylinder section and capable of reciprocating in the cylinder section. The cylinder section accommodates a bladder which is expanded and contracted when hydraulic oil is supplied to and discharged from it so that the piston can be pushed out. This bladder houses an insert die, the shape of which is identical with that of the internal structure of the bladder. An opening edge section of the bladder is contacted with pressure and fixed to between the insert die and the cylinder section. Hydraulic oil can be supplied to the bladder from the hydraulic path formed in the insert die. In this case, when a protrusion is formed in the bladder and an engaging groove to be engaged with the protrusion is formed in the insert die, the bladder can be fixed to the insert die so that the insert die cannot be drawn out. A notch step section is formed in the peripheral edge of the piston at which the piston is opposed to the bladder, and a soft protective member is arranged in this notch step section so that it can be opposed to the pushing peripheral edge of the bladder. It is preferable that an oil leakage detecting means is arranged on a sliding face of the piston in the cylinder section so as to detect the occurrence of damage of the bladder.
In another embodiment of a clamping device of the present invention, in a clamping device in which a stationary platen and a movable platen, which are connected with each other by tie rods, to which metallic molds are attached, can be fixed at a mold closing position by a platen lock means, a wall thickness changing plate means is provided between the platen lock means and the platen. A clamping device in which a stationary platen and movable platen, which are connected with each other by tie rods, to which metallic molds are attached, can be fixed to each other at a mold closing position by a platen lock means, comprises a wedge mechanism for adjusting a position of the platen lock means in the axial direction of the tie rod by the wedge action. The wedge mechanism is composed of a stationary wedge and movable wedge which are interposed between the platen lock means and the platen and come into contact with each other on an oblique face. In this arrangement, the wedge thickness may be changed by providing an insertion depth adjusting mechanism for adjusting an insertion depth of the movable wedge.
Further, the present invention provides a method of controlling an increase and decrease in clamping hydraulic pressure which will be described as follows. After a mold has been closed by a stationary platen and movable platen, which are connected with each other by tie rods, to which metallic molds are attached, hydraulic pressure is introduced into a pressurizing mechanism capable of pushing out a pressure plate attached to a platen body, the pressure plate being capable of coming into contact with and separating from the platen body, so that a clamping force is generated. In the case of increasing hydraulic pressure, a rotating speed of a piston pump is controlled so as to supply hydraulic oil to the pressurizing mechanism. After hydraulic pressure has increased to a clamping pressure, the hydraulic pressure is contained on the pressurizing mechanism side. After that, when a reverse speed of the piston pump is controlled, hydraulic pressure in a hydraulic oil path on the upstream side of the pressure containing position is gradually decreased. After the hydraulic pressure has been sufficiently decreased, the piston pump is stopped. In the case of decreasing hydraulic pressure, when a rotating speed of the piston pump is controlled, hydraulic oil is supplied to the pressurizing mechanism. Due to the foregoing, after the hydraulic pressure has increased to clamping pressure, hydraulic pressure in a hydraulic oil path on the upstream side of the containing position is increased from a state in which hydraulic pressure is contained on the pressurizing mechanism side until the pressures before and after the containing position become equal by operating the piston pump. After the containing state has been released, the reversing speed of the piston pump is controlled, so that hydraulic pressure in the hydraulic oil path on the upstream side of the containing position is gradually decreased and opened onto the tank side. In this way, a clamping force is controlled by increasing and decreasing pressure.
A method of releasing a mold of the present invention will be described as follows. A stationary platen and movable platen, which are connected with each other by tie rods, to which metallic molds are attached, open and close the metallic molds by an electrically driven ball screw mechanism. With respect to at least one of the platens, when hydraulic pressure is introduced into a bladder capable of being expanded and contracted or hydraulic pressure is introduced into a cylinder mechanism which moves forward and back by hydraulic pressure, a piston is pushed and clamping is conducted. While a screw member of the electrically driven ball screw mechanism is being supported by the platen being capable of moving in the axial direction, the screw member is restricted so that it cannot be rotated, and the ball screw member is moved in the axial direction by hydraulic force so as to generate a mold releasing force. In this case, when mold releasing is started, a brake means for restricting a rotation of the screw member is operated, and hydraulic oil is supplied from a clamping hydraulic source to a mold releasing cylinder mechanism for moving the ball screw member in the axial direction, so that a mold releasing operation is conducted. Next, the brake means is released, and the mold is opened by an electrical operation. After the mold opening motion has been completed, the mold releasing cylinder mechanism is returned to a position of the origin, and then hydraulic oil is enclosed in the mold releasing cylinder mechanism so that it cannot be moved.
The present invention will become more apparent in the accompanying drawings and the detailed description of preferred embodiments of the present invention.